A note of caution: There are many variables that determine air quality. Measuring the number of hours that a neighborhood experiences high levels of PM 2.5 is only one way of understanding the differences in air quality among areas in Los Angeles. Areas that have consistently high levels of PM 2.5, such as Chinatown and Downtown, are often close to major freeways. But the health profile of a neighborhood is made of many factors.

1. Chinatown

Based on this methodology, Chinatown had the most hours in which PM 2.5 levels rose above 100 on the AQI scale, at 147 out of a total of 6802.
The densely populated neighborhood is penned in by three busy freeways in the heart of the city.

2. Downtown. 116 hours.

No surprise here. This is the destination for hundreds of thousands of commuters and is crisscrossed by numerous freeways.

3. Lincoln Heights. 101 hours.

This area is on the other side of Interstate 5 from Chinatown and is ringed by hills, which can trap pollution.

4. Echo Park. 94 hours.

Sandwiched between Interstate 5 and the 101 freeway, Echo Park also gets a lot of traffic on its city streets from people traveling to and from Downtown.

5. Elysian Park. 93 hours.

Should we worry about the Dodgers? This neighborhood includes Dodger Stadium, and sits at the intersection of the 110 and 5 freeways.

Here’s a list of other neighborhoods which frequently register poor air quality based on our data:

How we did it:

We collect hourly readings of PM 2.5 levels (particles smaller than 2.5 µm in aerodynamic diameter) from the 12 monitoring stations of the Environmental Protection Agency and the South Coast Air Quality Management District located throughout Los Angeles County. The air quality data is updated every hour. The data we receive is based off of raw PM 2.5 measurements that have been converted to the Air Quality Index scale. PM 2.5 levels are generally proportional to AQI. (However, the actual AQI number is calculated using several different variables and is a 24-hour average.)

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We then use a process developed by our partners at the USC Spatial Sciences Institute that takes into account the surrounding geographic context of every neighborhood or area in the entire county of Los Angeles. We use geographic data from OSM (OpenStreetMap) to generate a “geographic abstraction” for each monitoring station automatically. The geographic abstraction is used to describe the neighborhood environment for a given location. For example, we compute the built environment, including the length of various road types, the point number of various locations types, area of open spaces, and so on. Then we build geo-context by selecting important features based on the air quality data.

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We create a fishnet of grid points across Los Angeles County. With the geo-context, we are able to compute PM2.5 values for the locations in the fishnet that do not have monitoring stations. We have around 3,000 points in total, four points within one square mile. For each point, we predict an hourly PM 2.5 AQI. We then map that against library of neighborhood boundaries created by The Los Angeles Times.
Have questions? Write us at askus@xtown.la

*This post was updated on June 21 to include language that better reflects the degree to which this analysis can be interpreted.